This page walks you through a simple demonstration of how CockroachDB replicates and distributes data. Starting with a 1-node local cluster, you'll write some data, add 2 nodes, and watch how the data is replicated automatically. You'll then update the cluster to replicate 5 ways, add 2 more nodes, and again watch how all existing replicas are re-replicated to the new nodes.
Before You Begin
Make sure you have already installed CockroachDB.
Step 1. Start a 1-node cluster
$ cockroach start --insecure \ --store=repdemo-node1 \ --host=localhost Step 2. Write data
In a new terminal, use the cockroach gen command to generate an example intro database:
$ cockroach gen example-data intro | cockroach sql --insecure CREATE DATABASE SET DROP TABLE CREATE TABLE INSERT 1 INSERT 1 INSERT 1 INSERT 1 ... In the same terminal, open the built-in SQL shell and verify that the new intro database was added with one table, mytable:
$ cockroach sql --insecure # Welcome to the cockroach SQL interface. # All statements must be terminated by a semicolon. # To exit: CTRL + D. > SHOW DATABASES; +--------------------+ | Database | +--------------------+ | information_schema | | pg_catalog | | intro | | system | +--------------------+ (4 rows) > SHOW TABLES FROM intro; +---------+ | Table | +---------+ | mytable | +---------+ (1 row) > SELECT * FROM intro.mytable WHERE (l % 2) = 0; +----+-----------------------------------------------------+ | l | v | +----+-----------------------------------------------------+ | 0 | !__aaawwmqmqmwwwaas,,_ .__aaawwwmqmqmwwaaa,, | | 2 | !"VT?!"""^~~^"""??T$Wmqaa,_auqmWBT?!"""^~~^^""??YV^ | | 4 | ! "?##mW##?"- | | 6 | ! C O N G R A T S _am#Z??A#ma, Y | | 8 | ! _ummY" "9#ma, A | | 10 | ! vm#Z( )Xmms Y | | 12 | ! .j####mmm#####mm#m##6. | | 14 | ! W O W ! jmm###mm######m#mmm##6 | | 16 | ! ]#me*Xm#m#mm##m#m##SX##c | | 18 | ! dm#||+*$##m#mm#m#Svvn##m | | 20 | ! :mmE=|+||S##m##m#1nvnnX##; A | | 22 | ! :m#h+|+++=Xmm#m#1nvnnvdmm; M | | 24 | ! Y $#m>+|+|||##m#1nvnnnnmm# A | | 26 | ! O ]##z+|+|+|3#mEnnnnvnd##f Z | | 28 | ! U D 4##c|+|+|]m#kvnvnno##P E | | 30 | ! I 4#ma+|++]mmhvnnvq##P` ! | | 32 | ! D I ?$#q%+|dmmmvnnm##! | | 34 | ! T -4##wu#mm#pw##7' | | 36 | ! -?$##m####Y' | | 38 | ! !! "Y##Y"- | | 40 | ! | +----+-----------------------------------------------------+ (21 rows) Exit the SQL shell:
> \q Step 3. Add two nodes
In a new terminal, add node 2:
$ cockroach start --insecure \ --store=repdemo-node2 \ --host=localhost \ --port=26258 \ --http-port=8081 \ --join=localhost:26257 In a new terminal, add node 3:
$ cockroach start --insecure \ --store=repdemo-node3 \ --host=localhost \ --port=26259 \ --http-port=8082 \ --join=localhost:26257 Step 4. Watch data replicate to the new nodes
Open the Admin UI at http://localhost:8080 and click View nodes list on the right. You'll see that all three nodes are listed. At first, the replica count will be lower for nodes 2 and 3. Very soon, the replica count will be identical across all three nodes, indicating that all data in the cluster has been replicated 3 times; there's a copy of every piece of data on each node.
Step 5. Increase the replication factor
As you just saw, CockroachDB replicates data 3 times by default. Now, in the terminal you used for the built-in SQL shell or in a new terminal, edit the default replication zone to replicate data 5 times:
$ echo 'num_replicas: 5' | cockroach zone set .default --insecure -f - range_min_bytes: 1048576 range_max_bytes: 67108864 gc: ttlseconds: 86400 num_replicas: 5 constraints: [] Step 6. Add two more nodes
In a new terminal, add node 4:
$ cockroach start --insecure \ --host=localhost \ --store=repdemo-node4 \ --port=26260 \ --http-port=8083 \ --join=localhost:26257 In a new terminal, add node 5:
$ cockroach start --insecure \ --host=localhost \ --store=repdemo-node5 \ --port=26261 \ --http-port=8084 \ --join=localhost:26257 Step 7. Watch data replicate to the new nodes
Back in the Admin UI, you'll see that there are now 5 nodes listed. Again, at first, the replica count will be lower for nodes 4 and 5. But because you changed the default replication factor to 5, very soon, the replica count will be identical across all 5 nodes, indicating that all data in the cluster has been replicated 5 times.
Step 8. Stop the cluster
Once you're done with your test cluster, stop each node by switching to its terminal and pressing CTRL-C.
If you do not plan to restart the cluster, you may want to remove the nodes' data stores:
$ rm -rf repdemo-node1 repdemo-node2 repdemo-node3 repdemo-node4 repdemo-node5 What's Next?
Use a local cluster to explore these other core CockroachDB features: